A trend in the construction industry has been to utilize smaller, more versatile machinery on the job-site. For example, mini-excavators and skid-steer loaders are often used to perform a variety of tasks. In many cases, a skid-steer loader or mini-excavator is equipped with an attachment for performing a particular task. Such attachments are typically powered by an auxiliary hydraulic circuit on the skid-steer loader or mini-excavator. Numerous attachments exist for performing a variety of tasks. For example, attachments exist for allowing a skid-steer loader to be used as a backhoe, an earth auger, an angle broom, a drop hammer, a snowplow, a brush saw, etc. These attachments typically are designed to be quickly connected and disconnected from the skid-steer loader or other machine by an operator on the job-site. The ability to quickly change attachments on the job-site makes these smaller machines more versatile than larger machines.
Quick-disconnect couplers are often used to allow quick and convenient connection and disconnection of hydraulic lines of an attachment to the auxiliary hydraulic circuit of the machinery. These types of couplers also are often used on construction equipment or agricultural tractors for connecting auxiliary circuits that power work tools or pull behind implements. The couplers are frequently housed in valve stacks or banks on the machinery in a position that is easily accessible to the operator when connecting an attachment. As such, the couplers are generally in close proximity of each other.
In general, an operator manually connects the hydraulic lines of an attachment to the auxiliary hydraulic circuit of the machine. To form the connection, a plug-like coupler part and a socket like coupler part are customarily used to couple the supply/return lines. In many instances, the connection is made while internal hydraulic pressure exists in one or both of the lines to be connected. Such internal hydraulic pressure can be residual hydraulic pressure from operating the attachment, or may be due to thermal hydraulic pressure buildup in the hydraulic circuit. Regardless, hydraulic pressure in the circuit can make forming the connection more difficult, especially with standard quick-disconnect couplers.
The ability of a coupler to connect and disconnect as intended to another coupler or fitting can be highly dependent on the system within which it operates, and specifically, the flow and pressure potential within the coupler. Many couplers have internal valves that are biased closed by internal hydraulic pressure when the coupler is not connected to another coupler or fitting. Once the coupler is connected to another coupler or fitting, the internal valve is opened allowing flow therethrough. For the user, it becomes increasingly difficult to make a connection as internal pressure, and thus hydraulic force, on the valves of the two couplers to be connected increases. In the hydraulic coupling industry, difficulty in making a connection due to hydraulic pressure is known as the “connect under pressure” problem.
Hydraulic pressure within a coupling is essentially a form of trapped energy. Thus, in order to connect a coupling under pressure, the trapped energy must be dissipated or otherwise managed. In general, this means that the energy within the coupling must be dissipated during the connection, or must be moved or contained in a place where its effects are minimized.
The majority of couplers capable of connecting under pressure do so by dissipating the internal hydraulic energy by allowing the hydraulic fluid (e.g. oil) to expand prior to connection. Some couplers have internal bleed valves that let the oil expand to a low-pressure line within the hydraulic system. Other couplers are designed with an internal bleed valve that lets the oil expand into and through the mating coupler. Still other couplers incorporate a mechanism for providing a mechanical advantage to generate enough force to overcome the hydraulic forces acting on the valves. And still other couplers have an external bleed valve that lets the hydraulic fluid expand external to the system, i.e., into the environment.
Many prior art coupler designs providing connect under pressure functionality have specialized internal valving that provides the connect under pressure functionality. Such couplers are more complex and cost more than a standard coupler (i.e., couplers without internal valving) due to the internal valving. Further, many prior art coupler designs utilize elastomeric seals that are required to throttle flow during connect under pressure. It is well known that throttling flow over elastomeric seals increases the potential for seal damage and often results in such. Many prior art coupler designs also involve the need for operator training as the operation of the couplers is not intuitive.